“In this paper, the temperature and humidity sensor DSl8820 is relatively simple to use and has high measurement accuracy, combined with the powerful functions and low power consumption characteristics of MSP430F2013, to design a node in a temperature-based wireless sensor network monitoring system to monitor the temperature of the environment. monitor. Wireless sensor networks have been favored by more and more academic departments, military departments, and industrial departments because of their huge scientific significance and use value.
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In this paper, the temperature and humidity sensor DSl8820 is relatively simple to use and has high measurement accuracy, combined with the powerful functions and low power consumption characteristics of MSP430F2013, to design a node in a temperature-based wireless sensor network monitoring system to monitor the temperature of the environment. monitor. Wireless sensor networks have been favored by more and more academic departments, military departments, and industrial departments because of their huge scientific significance and use value. With the development of social economy, it is necessary to detect and control the temperature and humidity of the environment in many cases, especially for places with serious pollution, harsh natural conditions, and hard-to-reach places.
1 Wireless sensor network structure
The wireless sensor network is composed of a large number of cheap small or micro wireless sensor network nodes deployed in the monitoring area, forming a multi-hop self-organizing intelligent network system through wireless communication. Its application prospects are very broad, and it is now gradually penetrating into various fields of human life, such as medical care, building structure, and health monitoring. Environmental detection is also a typical wireless sensor network application. The structure diagram is shown in Figure 1.
2 Design structure of temperature sensor node
The core of the wireless sensor network system is the sensor node, and the design needs to meet the following main conditions: network, miniaturization, low power consumption, and stability.
According to the above requirements, the sensor node design generally includes four parts: processor module, wireless transmission module, sensor module and power supply module. As shown in structure diagram 2:
In the hardware circuit design of this article, TI’s 16-bit low-power single-chip MSP430F2013 is used as the processing module, the sensor module uses DS18820, the wireless transmission module uses low-power wireless transceiver module CCll00, and the power supply uses a battery or a regulated power supply. The sensor module is responsible for the collection and data conversion of information in the monitoring area; the processor module is responsible for controlling the operation of the entire sensor node, storing and collecting data and data sent by other nodes; the wireless communication module is responsible for wireless communication and exchange with other sensor nodes Control messages and send and receive collected data; the power supply module provides the energy required for the operation of the sensor nodes, usually using micro-batteries.
2.1 DSl8820
The temperature sensor adopts DSl8820, which is relatively simple to use. Its main features are as follows
(1) Unique single-wire interface mode: When DS18820 is connected to the microprocessor, only one port line is needed to realize the two-way communication between the microprocessor and DS18820. No external components are required in use.
(2) The data line can be used for power supply, and the voltage range: +3.0~+5.5V.
(3) Temperature measurement range: -55+125℃. The inherent temperature measurement resolution is O. 5°C.
(4) 9-12 digits digital reading mode can be realized through programming.
(5) The user can set the non-volatile upper and lower alarm limits.
(6) Support multi-point networking function, multiple DS18820s can be connected in parallel on only three lines to achieve multi-point temperature measurement.
(7) Negative pressure characteristics. When the polarity of the power supply is reversed, the thermometer will not burn out due to heat, but it will not work normally.
Because DS18820 single-wire communication function is completed in time sharing, he has a strict concept of time slot, so read and write timing is very important. Various operations of the system to DS18820 must be carried out in accordance with the agreement. The operating protocol is: initialize DS18820 (send reset pulse) → send ROM function command → send memory operation command → process data.
2.2 MSP430F2013
The processor module is the computing core of the wireless sensor network node. All equipment control, task scheduling, energy calculation and function coordination, communication protocols, data integration and data dump procedures will be completed under the support of this module, so the processor’s Selection is very important in node design.
msp430f2013 is a microcontroller of TI’s msp430 series. It has the following structural characteristics: 16-bit risc cpu, 16-bit register and constant generator, which can obtain high code efficiency; five low-power modes, in Portable measurement applications can extend battery life: digitally controlled oscillator (dco) makes it takes less than μs to switch from low power consumption mode to normal mode; a 16-bit timer; 10 i/o ports: with synchronous communication Protocol (spi or i2c); a 16-bit σ-δ ADC. The structure of the sensor and processor is shown in Figure 3.
2.3 Wireless transceiver module CCl100
The wireless communication module is the main energy-consuming module, so choose it carefully. Considering that the communication module of the wireless sensor network node must be energy-controllable, and the power consumption of sending and receiving data should be very low, CCll00 of Chipcon Company is selected as the wireless transceiver module. The chip is small in size, low in power consumption, and the data rate supports programmable control from 1.2 to 500Kbps. In this article, CCll00 works at a frequency of 315MHZ, using FSK modulation, the data rate is 100kbps, and the channel interval is 100kHZ. The CCll00 programming line and the data line are respectively connected with the processor chip, so that the state of the CCll00 internal register can be easily read while sending and receiving data, so as to effectively control the communication process. The schematic diagram of the wireless transceiver module is as follows:
3 Node software design
The system software design mainly includes node sending program and parameter adjustment program, SINK node receiving program and host PC program. The node sending program mainly completes the data collection and data sending of the field sensor chip. The node sending program flow is shown in Figure 4. After power on, the node wireless module is in the receiving state, and it detects the command sent by the SINK node. After receiving the correct command, it starts to collect the field data. When the node receives the data, it will consider the data after the prefix as valid data. The MCU first checks the substation ID number. If the ID number is not the local machine, it discards all data and re-enters the receiving state, which can prevent wrong actions and maliciousness. Destruction. Otherwise, continue to judge the command number to determine the action of the node. If the SINK node needs data, the sensor number is judged to confirm which sensor data of the node is needed. After the data analysis is completed, the node collects, packs, and sends the field data to the SINK node, or starts the parameter adjustment system for parameter adjustment, and then enters the receiving state again.
4 Conclusion
On the basis of summarizing the original theoretical research results, this paper proposes a low-cost, low-power temperature wireless sensor network node based on the MCU MSP430 and CCllOO transceiver chip. In the experiment, 5 nodes and 1 SINK node can be used to form A small wireless sensor network. The successful design of the wireless sensor network node has laid a good foundation for the networking of the wireless sensor network to the final practical application.
The Links: LB070WV3-SD03 LQ10D131
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